Marinate the Portobello in the Italian Dressing, and set aside for 30 minutes. Mix the steak seasoning in with the ground turkey. Form into a patty, Put the Portobello, stem side down, and the Patty on the grill at the same time. When the patty no longer sticks to the grill it's time to flip it over. Flip the Portobello over at the same time and press it into the grill. (this will give it beautiful grill marks). Now would be a great time to Toast Your Buns!! (of course I meant the Hamburger Buns). When the Turkey burger is done put it on the bottom bun, pile the Portobello on top of it. I know it's so much bigger than the patty, but it's great. Spead the miracle whip and the mustard on the top bun, and you have heaven on your plate!!